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Tear Jerker: The Amazing Maurice and His Educated Rodents
Near the very end: "I'd hoped there was an island somewhere," said Dangerous Beans. "A place where rats could really be rats." This made me sob for five minutes, in spite of the generally happy conclusion of the book.
When Maurice and Dangerous Beans die. This troper bawled like a little kid, hit very hard with the fact that life was real, cruel, and didn't get storybook happy endings, for several minutes straight.